High frequency induction heater built in an injection mold

ABSTRACT

A high frequency induction heater built in an injection mold. The high frequency induction heater has a metal or silicon mold-insert, at least a heating module and at least a thermometer detector. The elements are reasonably fit with the mold-insert utilizing well-defined MEMS technology and UV-LIGA process. The high frequency induction heater is employed to apply a local heat for a microstructure of mold-insert during the micro molding process. By using the high frequency induction heater a fluid mold flow and high aspect ratio replication is achieved.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a high frequency induction heater builtin an injection mold for applying a local heat to the plastic, and morespecifically, to a high frequency induction heater formed on a side of astamper by micro electromechanical system (MEMS) technologies.

2. Description of the Prior Art

The injection compression molding technology has become mature in recentyears. The injection compression molding technology combines theinjection molding technology with the compression molding technology.The injection compression molding technology reduces the injectionpressure required when filling the plastic into the cavity. In addition,since the pressure of the melting plastic in the cavity is equallydistributed, thus a sink head or a warp problem is prevented. Therefore,the shrinkage of the product is well controlled, in light or theabove-mentioned advantages, the injection compression molding technologyis normally employed in fabricating optical precision moldings orcompact discs. For example, if the compact disc is fabricated byconventional injection molding technology, the plastic cannot be filledcompletely, which is known as short shot. Thus, thin moldings havinglarge areas, such as compact discs, cannot be formed by conventionalinjection molding technology. At present, the compact discs arefabricated by injection compression molding technology combining withhot runner design. Since the temperature of the plastic in the sprue isrelatively higher, the short shot problem is therefore avoided. U.S.Pat. No. 6,164,952 discloses a method or fabricating DVD discs usinginjection compression molding technology, in this patent, an inclinedangle design is adopted in the cavity for improving the fluidity of theplastic. It is possible to fabricate thin moldings having large areas(diameter: 120 mm; thickness: 0.6 mm) by injection compression moldingtechnology. However, if thinner moldings having larger areas and beingcoplanar (inclined angle design is not allowed) are desired, or diepattern of die stamper is more complicated (such as the molding includesvia holes), and the following problem may occur: If a single spruemethod is employed, the plastic cannot be completely filled into thecavity.

2. If a multiple sprue method is employed, and the temperaturedistribution of the molding is not equal, then the molding may havewarps after being cooling.

3. The plastic flow is obstructed and split so that a seam line willgenerate after the plastic flow converges.

4. Since the molding has large area and thin thickness, if the fluidityof the plastic is not good, the pattern of the microstructure in thestamper will be ruined by the applied pressure.

Generally speaking, 3D micro moldings require precise micro moldinginjection technology. At present, one of the methods to fabricate 3Dmicro moldings is carried out by a micro injection machine. The microinjection machine is one of the methods to fabricate complicated andmicro plastics, ceramics, and metal parts. Technologically, theinjection molding technology is the first choice for fabricating 3Dproducts with a complicated shape. Basically, the micro injectionmolding technologies are simply classified into 3 types: microstructureinjection molding technology, micrometer-level injection moldingtechnology, and micro injection molding technology. All of the threetechnologies have to overcome the problems such as micro injectionmachine design, micro mold manufacturing, micro mold flow analysis,micro injection process monitoring, etc. For example, the requirementsfor the processes of the micro injection machine are listed as follows:

1. An injection machine under 20 tons or a micro injection machine isrequired.

2. Short detention time is necessary for avoiding the degradation of theplastic.

3. Long injection stroke: the diameter of the screw must be as small aspossible (generally the diameter of the screw of the micro injectionmachine is 4 mm).

4. A long and thin plunger is required.

5. High shear stress is required to lower the viscosity of the plastic.

6. High injection pressure filling is required due to a high flowlength/wall thickness ratio and micro channel.

One of the largest shortcomings for the micro injection moldingtechnology is that a precise micro injection machine is required. Inaddition, the design and manufacturing of the micro injection mold isnot standardized yet, thus the number of the molding products cannotreach a mass amount during one single process.

In Japan Patent JP2000-218356, an external heater with sensors isemployed to detect the temperature of the movable mold-half and thestationary mold-half and to heat the movable mold-half and thestationary mold-half when the mold is open. Since the fluidity of themelting metal is improved, the metal moldings having complicatedstructure and large areas can be formed. However, if this method isemployed to form plastic moldings having complicated structure and largeareas, the following problems may occur:

-   -   1. Since the mold is heated when it is open, it is easy for the        mold to have an unequal temperature distribution.    -   2. This method is employed to inject metal material, thus the        temperature is too high for plastic materials.    -   3. This method heats the mold entirely, thus the mold cannot be        heated locally according to this method.    -   4. The mold is heated only when the mold is open, thus the mold        temperature is controlled by prediction.

In light of the above-mentioned problems, the present invention forms ahigh frequency induction heater on a side of the stamper by MEMStechnology. The high frequency induction heater provides two mainfunctions. First, the high frequency induction heater applies a localheat to sections of the plastic having a thin thickness or sectionshaving a large difference of cross sectional areas so that the plasticremains fluid. Second, when the temperature of the plastic molding isnot equally distributed, the high frequency induction heater can adjustthe overall temperature so that the temperature difference is reduced.

In MEMS industries, since the precise injection molding technology ismature and the cost of plastic material is cheap, polymers such asplastics are used to fabricate housings or covers. For a long time,optical wafers, bio wafers, and communication passive devices arefabricated by LIGA technology and hot embossing molding. Hans-DieterBauer et al. produces optical waveguide devices by LIGA technology andhot embossing molding. Since the refractive index is one of the keyfactors that influence the transmission of light, the precision andaccuracy of the size and relative position of the optical waveguidedevice is important. Generally speaking, the hot embossing molding canform the optical waveguide device. However, the hot embossing moldingtechnology cannot apply an equal pressure so that the moldings havingcomplicated structure and large areas are not easy to be formed. Inaddition, the production rate is not outstanding, and the microstructureof the hot embossing mold is easy to be broken when being pressurized.

The present invention forms a high frequency induction heater on a sideof the stamper such that moldings having a microstructure or largeareas, such as optical wafers, bio wafers, and communication wafers, canbe well defined. In combination with a substrate having MEMS devices orICs thereon, a wafer-level package can be made. In such case, the costof individual package will be enormously reduced.

SUMMARY OF INVENTION

It is therefore a primary objective of the present invention to providea high frequency induction heater built in a stamper of an injectionmold having a microstructure thereon. The magnetic permeability or theinduction heating ability of the material of the microstructure ishigher than that of the material of the stamper, thus the high frequencyinduction heater can apply heat to the microstructure through thestamper.

It is another objective of the present invention to form a highfrequency induction heater by MEMS technology on the stamper and apply alocal heat to the plastic such that sections of the plastic having athin thickness or sections having a large difference of cross sectionalareas remains fluid.

It is another objective of the present invention to solve the problemsof seamline, inadequate filling, and unequal temperature distribution ofthe moldings fabricated by conventional injection molding technology.

It is another objective of the present invention to solve the lowfluidity problem of the plastic due to thin thickness and to achievesub-millimeter lever injection molding.

It is another objective of the present invention to fabricatewafer-level plastic discs (6 to 8 inches), and perform wafer-levelpackaging in combination with substrates having ICs or MEMS devicesthereon.

It is another objective of the present invention to install a stamperand a high frequency induction heater on the movable mold-half, and toinstall a corresponding stamper on the stationary mold-half as well. Insuch case, 3D injection molding can be achieved to fabricate 3D moldingssuch as 3D gears by injection compression molding technology. Inaddition, the productivity is improved, and a micro injection machine isnot required.

These and other objects of the present invention will be apparent tothose of ordinary skill in the art after having read the followingdetailed description of the preferred embodiment that is illustrated inthe various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an injection mold of the presentinvention.

FIG. 2 is a schematic diagram of a high frequency induction heatingmodule of the present invention.

FIG. 3 and FIG. 4 are schematic diagrams of the high frequency inductionheating module and a stamper.

FIG. 5 to FIG. 12 are schematic diagrams illustrating steps of formingthe high frequency induction heater according to the present invention.

FIG. 13 is a schematic diagram illustrating the distribution of platinumresistance thermometer detectors (RTD) according to the presentinvention.

FIG. 14 is a schematic diagram illustrating micro channels of a biochip.

FIG. 15 and FIG. 16 are schematic diagrams illustrating a coupler ofoptical fiber.

FIG. 17 is a schematic diagram of an injection mold for injecting amicro gear.

FIG. 18 is a schematic diagram illustrating bottom cavities of theinjection mold shown in FIG. 17.

FIG. 19 is a schematic diagram illustrating a runner of the injectionmold shown in FIG. 17.

FIG. 20 is a local amplified diagram of the injection mold shown in FIG.19.

FIG. 21 is a schematic diagram illustrating the distribution of the highfrequency induction heating coils according to another embodiment of thepresent invention.

DETAILED DESCRIPTION

Please refer to FIG. 1 and FIG. 2. FIG. 1 is a schematic diagram of aninjection mold of the present invention. FIG. 2 is a schematic diagramof the high frequency induction heating module of the present invention.As shown in FIG. 1 and FIG. 2, the injection mold comprises a stationarymold-half 03, a movable mold-half 04, a stamper 34, and a high frequencyinduction heating module 23 installed on the movable mold-half 04 forapplying a local heat to the plastic flowing in a cavity 22. In suchcase, the plastic is heated and remains fluid. The high frequencyinduction heating module 23 comprises a plurality of thermometerdetectors 25, a plurality of high frequency induction heating coils 26,a plurality of via holes 27, and an external power circuit terminal 28.It is worth noting that there are several ways to arrange the relativeposition of the high frequency induction heating module 23 and thestamper 34. For example, please refer to FIG. 3. FIG. 3 is a schematicdiagram of the high frequency induction heating module 23 and thestamper 34. As shown in FIG. 3, the high frequency induction heatingmodule 23 is formed on one side of the stamper 34, and themicrostructure of the cavity 22 is formed on the other side of thestamper 34. Therefore, the high frequency induction heating module 23and the stamper 34 are a uniform-forming structure. In another example,please refer to FIG. 4. FIG. 4 is another schematic diagram of the highfrequency induction heating module 23 and the stamper 34. As shown inFIG. 4, the high frequency induction heating module 23 and the stamper34 are fabricated separately.

The details of the above-mentioned embodiments are shown as follows.First, a mold flow analysis is performed to decide the sprue method, theamount and position of sprues. Also in the mold flow analysis, theflowing condition of the plastic and the temperature/pressuredistributions are observed for knowing where the thickness is thinner orwhere the seamline occurs easily. For example, if the thin molding haslarge areas, a multi sprues method is adopted. If necessary, a hotrunner is also required.

Then a layout design of high frequency induction heating coils 26 iscarried out. The position of the high frequency induction heating coils26 is decided according to the temperature distribution of the moldflow. Since the high frequency induction heating coils 26 can bearranged in circles, and a plurality of thermometer detectors 25, suchas platinum resistance thermometer detector (RTD), can be installed ifnecessary. Each high frequency induction heating coil 26 is controlledby an external power circuit (not shown). The desired heatingtemperature is controlled by the thermometer detectors 25 so thatdeformation of molding products due to high temperature difference isprevented.

As shown in FIG. 3, three sets of high frequency induction heating coils26 are arranged spirally. However, the arrangement of the high frequencyinduction heating coils 26 is not limited by this embodiment. Inaddition, the number of the heating coils 26 and the external powercircuits can also be changed. Any designs that can apply a local heatand control the overall temperature of the stamper 34 for preventing theseamline is allowed. The high frequency induction heating coils 26generate a magnetic field for heating the microstructure of the stamper34. Generally, copper (Cu) is selected as the material of the highfrequency induction heating coils 26. The more and the closer the highfrequency induction heating coils 26 are, the stronger the magneticfield is. And therefore the heating ability is better. It is worthnoting that all the high frequency induction heating coils 26 areinsulated by the thick photoresist pattern (SU8), thus neighboringdevices will not be affected by the heat.

As shown in FIG. 2, since the high frequency induction heating coils 26are insulated by the thick photoresist pattern 29, a plurality of viaholes 27 are formed, a copper layer are formed as a conductive layer,and an external power circuit terminal 28 is formed so that the highfrequency induction heating coils 26 and the external power circuits areconnected.

It is worth noting that the mold is not completely clamped until theplastic is fully filled. When the plastic is entirely filled into thecavity 22, a clamp unit (not shown) is used to apply a pressure to thecavity 22 for compressing the plastic. And the pressure is held afterthe plastic is filled.

Please refer to FIG. 5 to FIG. 12. FIG. 5 to FIG. 12 are schematicdiagrams illustrating steps of forming the high frequency inductionheater according to the present invention. As shown in FIG. 5, analuminum substrate 24 is provided. Then a low pressure chemical vapordeposition (LPCVD) process is performed to deposit a silicon dioxide(SiO₂) layer 30 on the aluminum substrate 24 as an insulating layer.Please note that other insulating materials such as nitride can also beselected as the insulating layer. The aluminum substrate 24 is selecteddue to its high rigidity and lower induction heating ability of highfrequency comparing to iron and nickel. On the contrary, a siliconsubstrate is not suitable for the present invention due to itsfragility.

As shown in FIG. 6, a platinum layer (not shown) is formed by depositingon the aluminum substrate 24, and a lithography process (photo-etchingprocess) including coating a photoresist pattern, exposing, developing,and etching is performed to form a plurality of thermometer detectors25. Then another SiO₂ layer 30 or a nitride layer is deposited to coverthe thermometer detectors 25, and a chemical vapor polishing (CMP)process is performed to planarize the SiO₂ layer 30.

As shown in FIG. 7, a thick photoresist pattern 29 with highsolidification strength is coated an exposure process and a developmentprocess are performed, and then a reactive ion etching (RIE) process isperformed to form a plurality of via holes 27 connecting to thethermometer detector 25. Following that, an electroforming process isperform to electroform a copper pattern (not shown) for forming aplurality of high frequency heating coils 26 and the plurality of viaholes 27 connecting to the thermometer detectors 25. Finally, a CMPprocess is performed to planarize the surface.

As shown in FIG. 8, thick photoresist pattern 29 with highsolidification strength is coated, and an exposure process and adevelopment process are performed. Then an electroforming process isperformed to form the plurality of via holes 27. Then, a CMP process isperformed to planarize the surface.

As shown in FIG. 9, the thick photoresist pattern 29 with highsolidification strength is coated, an exposure process and adevelopment, process are performed, and an electroforming process isperformed to form the high frequency induction heating coils 26. Then, aCMP process is performed to planarize the Surface.

As shown in FIG. 10, the thick photoresist pattern 29 with highsolidification strength is coated, an exposure process and a developmentprocess a performed, and an electroforming process is performed to formthe high frequency induction heating coils 26 and an external powercircuit terminal 28. Then, a CMP process is performed to planarize thesurface.

As shown in FIG. 11, the aluminum substrate 24 is turned over, and aphoto-etching process is performed to form a photoresist pattern 29A andto etch the aluminum substrate 24. Then, an iron/nickel electroformingprocess is performed to form a microstructure 22.

As shown in FIG. 12, a CMP process is performed to planarize the surfaceso that a high frequency induction heater built in an injection mold isfabricated.

In the above embodiment, the aluminum substrate 24 is selected as anexample. However, other substrates having proper rigidity, conductivity,and magnetic conductivity, such as nickel substrate, can be adopted inthe present invention.

In addition, the stamper 34 and the high frequency induction heatingmodule 23 can be fabricated separately. In such case, after the externalpower circuit terminal 28 is formed, a polishing process can be carriedout to fabricate the high frequency induction heater.

Please refer to FIG. 13. FIG. 13 is a schematic diagram illustrating thedistribution of platinum resistance thermometer detectors (RTD) 25according to the present invention. As shown in FIG. 13, a plurality ofplatinum RTDs 25 are positioned in places where the thickness is smallfor applying heat to the plastic so that the plastic remains fluid.

The injection mold having a high frequency induction heater can beemployed to fabricate various moldings having a microstructure thereon.Please refer to FIG. 14. FIG. 14 is a schematic diagram illustratingmicro channels of a bio chip. The bio chip is for separating differentbio polymers. The bio chip comprises cavities 22 and micro channels 31on the surface, and micro electrodes 32 or micro heating module (notshown) on the bottom. Considering the hydrophile/hydrophobe and thebiocompatibility problems, polymers are preferred as the material of biochips. At present, the cross-sectional area of the micro channel 31 isabout 20 μm² to 50 μm² while tracking depth of compact discs is only 0.5μm, thus microstructure such as the micro channel 31 can be fabricatedby injection compress molding technology.

The present invention can also be employed to fabricated couplers ofoptical fiber. Since the coupler is mostly made of ceramics, if astamper 34 fabricated by MEMS technology and LIGA technology is used toform the coupler, the production cost of optical fiber devices will bereduced. Please refer to FIG. 15 and FIG. 16. FIG. 15 and FIG. 16 areschematic diagrams illustrating a coupler of optical fiber. As shown inFIG. 15 and FIG. 16, the coupler comprises an optical fiber cavity 38for placing an optical fiber 40, and a waveguide cavity 39. Thewaveguide cavity 39 is filled with a material identical to a core 41 ofthe optical fiber 40 for being a transmitting medium of optical signals.When the optical fiber 40 is introduced, the core 41 and a waveguide 42are aligned correctly so that optical signals are transmitted outthrough the waveguide 42.

Furthermore, the injection compression molding technology of the presentinvention can be adopted to fabricate micro gears for solving the poorfluidity problem. Please refer to FIG. 17 to FIG. 19. FIG. 17 is aschematic diagram of a gear injection mold. FIG. 18 is a schematicdiagram illustrating bottom cavities 22A of the injection mold shown inFIG. 17.FIG. 19 is a schematic diagram illustrating a runner 20 of theinjection mold shown in FIG. 17. As shown in FIG. 17, the meltingplastic is ejected from a sprue 19, and flows to the cavities 22 throughthe runner 20. When the plastic flows through the stationary mold-half03 and the movable mold-half 04, the plastic is cooled down thus thefluidity is reduced. In such case, the plastic cannot pass through thegate 21 so that the cavities 22 are not well filled. Therefore, a highfrequency induction heating module (not shown) is installed to apply alocal heat to the plastic for improving the low fluidity problem.

As shown in FIG. 18 and FIG. 19. The high frequency induction heatingmodule 23 and the bottom cavities 22A are formed separately, andcombined with the stationary mold-half 04. Top cavities (not shown) areinstalled on the movable mold-half 03. The high frequency inductionheating module 23 can apply a local heat to the plastic and control theoverall temperature distribution such that the temperature difference isreduced.

Please refer to FIG. 20 and FIG. 21. FIG. 20 is a local amplifieddiagram of the injection mold shown in FIG. 19.FIG. 21 is a schematicdiagram illustrating the distribution of the high frequency inductionheating coils 26. This embodiment is similar to the first embodiment ofthe present invention. The difference between these two embodiments isthe position of the high frequency induction heating module 23. In thisembodiment, a multiple cavities injection mold for forming a pluralityof parts is illustrated. Therefore, the production cost is reduced.

Those skilled in the art will readily appreciate that numerousmodifications and alterations of the device may be made withoutdeparting from the scope of the present invention. Accordingly, theabove disclosure should be construed as limited only by the metes andbounds of the appended claims.

1. A high frequency induction heater built in an injection moldcomprising: at least a stamper, fabricated by micro electromechanicalsystem (MEMS)technologies, having a micro pattern of a micro system; atleast a high frequency induction heating module, fabricated by MEMStechnologies, positioned on a side of the stamper, the high frequencyinduction heating module comprising at least a set of high frequencyinduction heating coils, the high frequency induction heating modulebeing controlled by a driver positioned outside the injection mold; andat least a set of thermometer detectors, fabricated by MEMStechnologies, positioned between the set of high frequency inductionheating coils, the set of thermometer detectors being controlled by atemperature controller positioned outside the injection mold; whereinthe high frequency induction heating module emits electromagnetic waveswhich penetrate the stamper and applies a local heat to a plastic suchthat sections of the plastic having a thin thickness or sections havinga large difference of cross sectional areas remains fluid, in such casethe micro pattern of the micro system is accurately transferred to theplastic by injection compression molding technologies.
 2. The highfrequency induction heater of claim 1 wherein the MEMS technologiescomprise the following steps: (a) depositing an oxide layer or a nitridelayer onto a metal substrate as an insulating layer; (b) depositing aplatinum layer, and performing a photo-etching process which includescoating a photoresist pattern, exposing, developing, and etching, fordefining a thermometer detector pattern; (c) depositing an oxide layeror a nitride layer as an insulating layer to cover the thermometerdetector pattern; (d) coating a thick photoresist pattern with highsolidification strength, performing an exposure process and adevelopment process, electroforming a copper layer to a desirableheight, and performing a chemical mechanical polishing (CMP) process toplanarize the copper layer for forming the set of high frequencyinduction heating coils; (e) coating a thick photoresist pattern withhigh solidification strength, performing an exposure process and adevelopment process, electroforming a copper layer to a desirableheight, and performing a CMP process to planarize the copper layer forforming via boles; (f) coating a thick photoresist pattern with highsolidification strength, performing an exposure process and adevelopment process, electroforming a copper layer to a desirableheight, and performing a CMP process to planarize the copper layer forforming an external power circuit; and (g) polishing the metalsubstrate.
 3. The high frequency induction heater of claim 2 wherein thestamper and the high frequency induction heater are fabricatedindividually or jointly, and if the stamper and the high frequencyinduction heater are fabricated jointly, then step (g) is furtherdefined by the following steps: turning the metal substrate over;performing a photo-etching process to etch the metal substrate;performing an electroforming process to form a magnetic layer comprisingiron and nickel for forming a microstructure; and performing a CMPprocess to planarize the magnetic layer for forming an insert moldhaving a built-in high frequency induction heater.
 4. The high frequencyinduction heater of claim 1 wherein a microstructure is inserted intothe stamper by MEMS electroforming technologies, and the high frequencyinduction heater positioned under the microstructure or the stamper iscapable of applying the local heat and controlling an overalltemperature so that the plastic is fluid and a deformation due to atemperature difference is prevented.
 5. The high frequency inductionheater of claim 4 wherein a material of the microstructure is a metalidentical to that of the stamper or a metal differing from that of thestamper, the material identical to that of the stamper is forcontrolling the overall temperature, the metal differing from that ofthe stamper is for applying the local heat, if the material of themicrostructure differs from that of the stamper, the microstructure thenhas a higher magnetic permeability or a higher induction heating abilitythan the stamper.
 6. The high frequency induction heater of claim 1wherein the set of high frequency induction heating coils are positionedunder a surface of the high frequency induction heater, thus amulti-level interconnect technology is adopted to locate the externalpower circuit in a bottom layer, and only a microstructure of the set ofhigh frequency induction heating coils is exposed in an upper layer. 7.The high frequency induction heater of claim 1 being capable of beingpositioned in a stationary mold-half and/or in a movable mold-half. 8.The high frequency induction heater of claim 1 wherein the highfrequency induction heater and the thermometer detectors are control ledby a plurality of drivers and temperature controllers operatingindividually.
 9. The high frequency induction heater of claim 1 beingcapable of fabricating wafer-level plastic discs (6 inches to 8 inches)by injection compression molding technologies, and further performing awafer-level package process on a substrate having ICs or MEMS elements.